Hops have been used for centuries to flavor beer and are considered, along with water, yeast, and malt, to be an essential ingredient. Since the sixties, following elucidation of the structure of the hop bittering compounds in the fifties by such pioneering investigators as Rigby and Verzele, various forms of chemically modified hop extracts have found their way into commercial application.
A goal of present brewing technology is to make reproducible brews. Difficulties are encountered at every stop in the brewing process: unwanted variations in yeast cultures, in hops, in malt, in adjuncts, and even in times, temperatures, and the human element of the brewhouse. Beer presents a subtle combination of carbonation, foam, mouth feel, bitterness, and aroma when smelled and swallowed. Whatever can be done to improve the reproducibility and control of even one variable--yeast, hops, malt, adjuncts--is exceptionally important.
Hop flavors have attracted widespread interest in recent years for use in controlling and standardizing the flavoring of beer including ale, especially by post-fermentation treatment.
U.S. Pat. No. 4,778,691 teaches that unidentified hop-derived substances, when present during fermentation, are either metabolized or removed by the yeast. However, when they are added post-fermentation, they complex or esterify with the alcohol present to give the undesirable fruity-estery-fatty or stout type of aromas during normal storage of the beer. Therefore, such a flavored fresh beer may be acceptable, but one aged for several weeks may not.
U.S. Pat. No. 4,778,691 also states that the prior art is not effective in removing the undesirable impurities. For example, Todd (U.S. Pat. No. 4,002,683) removes humulinic acid, tannins, sugars, and gushing promoters. Humphrey (U.S. Pat. No. 4,302,479) performs a highly-acidic wash of an organic solvent solution of extract. Neither procedure, because of the very acidic pH used for purification, will remove neutral materials. Lance (U.S. Pat. No. 4,395,431) elutes these substances with the alpha acids, and does not remove or separate them. Westermann (U.S. Pat. No. 3,798,332), concentrates them with his so-called pure isoalpha acids. The procedure of Humphrey (U.S. Pat. No. 3,875,316) also does not remove them.
In contrast, U.S. Pat. No. 4,778,691 teaches the extraction of impurities by agitating the hop flavor with water at a pH of 4 to 12 and extracting the impurities from the organic phase into the aqueous phase.
Although there has been some research into the removal of undesirable odors and odor-forming compounds from hop flavors, there is a continuing search for more efficient, effective methods.